Q: Our veterinarian recently told us about a little boy who lost his sight in one eye because of a roundworm infection, which he might have gotten from his puppy. We were thankful that our veterinarian told us about this and that she recommended periodic stool sample checks to be sure that our dog does not have internal parasites.

Are roundworms commonly diagnosed in puppies?

A: Unfortunately, finding roundworms in puppies is fairly common. It is interesting that puppies can become infected with roundworms while still being carried in the uteri of their mothers before birth. It is also common for puppies to become infected with roundworms while nursing through ingestion of contaminated milk and by living in contaminated environments.

After a roundworm egg is ingested, it develops into a larva in the intestines of the dog. Roundworm larvae eventually migrate out of the intestines, burrow through the liver, and end up in the lungs of the infected dog. Larvae in the lungs eventually get coughed up into the oral cavity and then swallowed. The swallowed larvae develop into adult roundworms in the intestines of the dog. Adult roundworms shed eggs, which pass into the environment when the infected dog defecates. The development of new larvae and the migration through the tissues of the dog is repeated when another dog ingests the contaminated feces from the first dog. This is one reason that all responsible dog owners always pick up the stools of their dogs and dispose of them properly.

Unfortunately, canine roundworms can infect humans. When children ingest stools from infected dogs or contaminated dirt or sand where infected dogs have defecated, the development of larvae can occur within them. Occasionally, these larvae end up in the eye and cause blindness. This is a good reason to teach children to wash their hands before eating and to never put their hands in their mouths. Likewise, people should not allow dogs to lick them in the face.

The fear of roundworms should not keep families from enjoying the companionship of their dogs. However, all dog owners should have their pets examined for parasites on a regular basis and should be diligent about picking up and disposing of their dog's stools. Your veterinarian can give you additional advice about the prevention of worms in your dog.

Q: Our 6-year-old, mixed-breed dog becomes very aggressive whenever we try to trim his nails. He tries to bite us and usually throws quite a fit. As far as I know we have never hurt him or caused any bleeding while trimming his nails.

What can we do?

A: Your experience while trimming your dog's nails is not unusual. Dogs that vigorously resist having their toenails trimmed at home should be taken to a veterinarian for trimming. Most veterinarians have technicians who can safely restrain these dogs without hurting them and can quickly control bleeding if the nails are accidentally trimmed too short. Dogs often act differently if in a strange environment and being handled by unfamiliar people. Neither you nor your dog should have to suffer while doing a routine nail trim.

Send an e-mail or write to Pets, P.O. Box 120190, San Diego, CA 92112-0190. Only questions of general interest will be answered in this column.